Background: This study aimed to analyze the effects of preoperative oral intake of liquid carbohydrate on postoperative blood glucose, fasting-thirst, and fatigue levels in patients undergoing arthroscopic surgery. Methods: This randomized controlled clinical trial enrolled 82 patients, who were scheduled to undergo arthroscopic surgery, and divided them into two groups: (1) those who consumed a carbohydrate-rich drink, and (2) those not consuming anything after midnight. Pre- and postoperative fasting-thirst (visual analog scale) and blood glucose levels were measured. Likewise, the Brief Fatigue Inventory was applied to patients 24 hours after surgery. Results: The mean blood glucose levels in the first postoperative hour were 90.90 +/- 13.56 mg.dL-1 and 107.00 +/- 15.84 mg.dL-1 in the intervention group and control group, respectively (p < 0.001). The postoperative mean thirst scores were 4.70 +/- 1.59 and 6.36 +/- 2.07 in the intervention group and control group, respectively (p < 0.001). Their corresponding postoperative mean fasting scores were 5.54 +/- 1.76 and 5.86 +/- 1.79 (p > 0.05) and the mean fatigue levels in the 24th postoperative hour were 4.80 +/- 2.13 and 5.48 +/- 1.46, respectively (p > 0.05). Conclusions: Oral intake of liquid carbohydrate before spinal anesthesia was found to have positive effects on patients' postoperative blood glucose and thirst levels. (c) 2021 Sociedade Brasileira de Anestesiologia. Published by Elsevier Editora Ltda. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).